The present invention relates to a polishing cloth which is attached to a base plate of a polishing machine so as to hold a workpiece (e.g., a semiconductor wafer) in place while the workpiece is polished, and a method for attaching/detaching the polishing cloth to/from the base plate of the polishing machine.
In recent years, in the semiconductor industry, the integration level of ICs has rapidly increased. It has increased from 4M to 16M and is now proceeding to the 64M level.
In light of the above circumstances, improvement in the surface quality of a wafer (on which ICs are formed) has been demanded under stringent cost restraints. In order to increase the integration level of ICs, it is necessary to reduce the minimum width that is allowed for devices to be mounted on the wafer, as well as improving the chemical and electrical properties of the wafer. The ideal value for the minimum width has shifted from about 0.5 microns to about 0.35 microns. Moreover, the wafer size has rapidly increased, followed by a rapid reduction in cost per bit. The increase in wafer size has also resulted in a remarkable increase in the size of machines used for processing wafers. For example, in a polishing process for mirror-finishing a wafer surface, a polishing machine with a base plate having a diameter of about 42 inches is used to polish 5xe2x80x2-diameter wafers, whereas a polishing machine with a base plate having a diameter as large as about 59 inches is used to polish 8xe2x80x2-diameter wafers. In general, the polishing of wafers is achieved by causing friction with a polishing cloth in the presence of a polishing slurry, while the polishing cloth is retained on a lower base plate of a polishing machine and the wafer to be processed is retained on an upper base plate of the polishing machine.
Accordingly, the size of the polishing cloth is typically the same as that of the lower base plate of the polishing machine. Specifically, a polishing cloth with a diameter of about 42 inches is generally used for polishing 5xe2x80x2-diameter wafers, whereas a polishing cloth with a diameter of about 59 inches is used for polishing 8xe2x80x2-diameter wafers.
In general, the polishing cloth is secured to the base plate of the polishing machine with a high-performance double-sided adhesive tape (i.e., a tape having adhesive layers on the both sides). In this securing method, however, the adhesive layer provided on the back face of the polishing cloth is adhered to the base plate surface so firmly that a tack strength as large as about 2 to 3 kg/inch width exists when the polishing cloth thus attached to the base plate must be detached in a usual manner. In other words, a force up to about 156 kg may be required to detach a polishing cloth from a base plate having a diameter of about 42 inches, and a force up to about 180 kg may be required to detach a polishing cloth from a base plate having a diameter of about 59 inches. Thus, it is very troublesome when a used polishing cloth must be exchanged with a new one.
On the other hand, if a polishing cloth fails to be attached in proper alignment with respect to the base plate, it has been difficult to reposition and reattach the polishing cloth.
A polishing cloth according to the present invention includes: a polishing cloth substrate; a first pressure-sensitive adhesive layer formed on a back face of the polishing cloth substrate; a support formed on a back face of the first pressure-sensitive adhesive layer; a second pressure-sensitive adhesive layer formed on a back face of the support; and a release sheet releasably attached to the second pressure-sensitive adhesive layer, wherein the second pressure-sensitive adhesive layer includes an adhesive composition, the adhesive composition containing a pressure-sensitive adhesive and a side-chain crystallizable polymer so that the side-chain crystallizable polymer is present in an amount of about 1% to about 30% by weight based on the adhesive composition, and the side-chain crystallizable polymer including as a main component thereof an acrylic acid ester and/or methacrylic acid ester which has a straight-chain alkyl group including 16 or more carbon atoms as a side chain.
In one embodiment of the invention, the adhesive composition contains a tackifier in an amount of about 10% to about 30% by weight; and the adhesiveness of the adhesive composition is decreased by more than about 90% when heated above about 50xc2x0 C.
In another embodiment of the invention, the side-chain crystallizable polymer has a molecular weight of about 2,000 to about 15,000.
In still another embodiment of the invention, the side-chain crystallizable polymer has a melting point which occurs within a temperature range narrower than about 15xc2x0 C.
Alternatively, the polishing cloth according to the present invention includes: a polishing cloth substrate; a pressure-sensitive adhesive layer formed on one face of the polishing cloth substrate; and a release sheet releasably attached to the pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer includes an adhesive composition, the adhesive composition containing a pressure-sensitive adhesive and a side-chain crystallizable polymer so that the side-chain crystallizable polymer is present in an amount of about 1% to about 30% by weight based on the adhesive composition, and the side-chain crystallizable polymer including as a main component thereof an acrylic acid ester and/or methacrylic acid ester which has a straight-chain alkyl group including 16 or more carbon atoms as a side chain.
In one embodiment of the invention, the adhesive composition contains a tackifier in an amount of about 10% to about 30% by weight; and adhesiveness of the adhesive composition is decreased by more than about 90% when heated above about 50xc2x0 C.
In another embodiment of the invention, the side-chain crystallizable polymer has a molecular weight of about 2,000 to about 15,000.
In still another embodiment of the invention, the side-chain crystallizable polymer has a melting point which occurs within a temperature range narrower than about 15xc2x0 C.
In another aspect of the invention, there is provided a method for attaching/detaching any one of the above polishing cloths to/from a base plate of a polishing machine, including the steps of: attaching the polishing cloth to the base plate of the polishing machine by allowing the pressure-sensitive adhesive of the polishing cloth to the base plate surface maintained at temperature T1; and detaching the polishing cloth from the base plate maintained at temperature T2 which is higher than temperature T1.
The present invention provides the following effects.
According to one embodiment of the present invention, a polishing cloth is provided which includes an adhesive layer composed essentially of an adhesive composition containing a pressure-sensitive adhesive and a side-chain crystallizable polymer, where the side-chain crystallizable polymer is present in the amount of about 1% to about 30% by weight based on the adhesive composition. The side-chain crystallizable polymer includes as a main component thereof an acrylic acid ester and/or methacrylic acid ester which has a straight-chain alkyl group including 16 or more carbon atoms as a side chain. As a result, the polymer is capable of shifting between a crystal state and an amorphous state in a reversible manner, responsive to a relatively small temperature change from an arbitrarily selected ordinary temperature value; consequently, the polymer exhibits drastic a change in its tackiness to the base plate surface.
Thus, when the polishing cloth is heated to a predetermined elevated temperature (e.g., about 50xc2x0 C. to about 100xc2x0 C.), the adhesiveness of the adhesive layer rapidly decreases. Therefore, at the time of exchanging polishing cloths, the base plate and/or the polishing cloth may be heated so as to greatly decrease the adhesiveness of the adhesive layer with respect to the base plate surface, whereby the polishing cloth can be easily peeled off the base plate surface.
In accordance with an embodiment of the invention where the adhesive composition contains a tackifier in the amount of about 10% to about 30% by weight and where the adhesiveness of the adhesive composition is decreased by more than about 90% when heated above about 50xc2x0 C., a predetermined level of adhesiveness with respect to the base plate surface can be retained at ordinary temperatures, whereas a rapid decrease in adhesion strength can be caused by heating. Thus, a tackifier present in the above-mentioned amount will not substantially influence the temperature sensitivity of the polymer. As a result, the adhesive composition according to the present invention exhibits a sufficient adhesion strength at ordinary temperatures, while maintaining a good balance between the adhesion strength at ordinary temperatures and the peeling force required at elevated temperatures.
Thus the invention described herein makes possible the advantages of (1) providing a polishing cloth which adheres strongly, stably, and precisely to a base plate of a polishing machine while a wafer or the like is polished with the polishing cloth, and yet allows for easy detachment from the base plate; (2) providing a method for attaching/detaching such a polishing cloth to/from a base plate of a polishing machine; (3) providing a polishing cloth which can be easily repositioned and reattached for proper alignment with respect to a base plate of a polishing machine; and (4) providing a method for attaching/detaching such a polishing cloth to/from a base plate of a polishing machine.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.